Large Radius Probe

ABSTRACT

A large radius probe for a surface analysis instrument such as an atomic force microscope (AFM). The probe is microfabricated to have a tip with a hemispherical distal end or apex. The radius of the apex is the range of about a micron making the probes particularly useful for nanoindentation analyses. The processes of the preferred embodiments allow such large radius probes to be batch fabricated to facilitate cost and robustness.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.15/935,937, filed Mar. 26, 2018 (U.S. Pat. No. 10,802,045, issued Oct.13, 2020), which is entitled Large Radius Probe. The subject matter ofthis application is hereby incorporated by reference in its entirety.

BACKGROUND OF THE INVENTION Field of the Invention

The preferred embodiments are directed to a probe device for a metrologyinstrument and a corresponding method of manufacture, and moreparticularly, a large radius atomic force microscope (AFM) probe devicethat can be batch fabricated and is particularly adapted fornanoindentation measurements.

Description of Related Art

Scanning probe microscopes (SPMs), such as the atomic force microscope(AFM), are devices which use a sharp tip and low forces to characterizethe surface of a sample down to atomic dimensions. Generally, the tip ofthe SPM probe is introduced to the sample surface to detect changes inthe characteristics of the sample. By providing relative scanningmovement between the tip and the sample, surface characteristic data canbe acquired over a particular region of the sample and a correspondingmap of the sample can be generated.

Most AFMs employ sharp tipped probes (radius less than 10 nm) for highresolution. Some applications require a probe with a larger tip radius,however. Nanoindentation using an AFM is one such application.Nanoindentation is used to conduct mechanical property tests, such asthe hardness or modulus of a sample. Typically, when performingnanoindentation measurements, an AFM monitors force displacement of thetip to provide an indication of Young's modulus. AFM can also performnano-scratching and wear testing to investigate material adhesion anddurability.

An overview of AFM and its operation follows. A typical AFM system isshown schematically in FIG. 1. An AFM 10 employing a probe device 12including a probe 14 having a cantilever 15. XYZ scanner generatesrelative motion between the probe 14 and sample 22 while theprobe-sample interaction is measured. In this way images or othermeasurements of the sample can be obtained. XYZ scanner is typicallycomprised of one or more actuators that usually generate motion in threeorthogonal directions (XYZ). Often, XYZ scanner is a single integratedunit that includes one or more actuators to move either the sample orthe probe in all three axes, for example, a piezoelectric tube actuator.Alternatively, the scanner may be an assembly of multiple separateactuators. Some AFMs separate the scanner into multiple components, forexample an XY scanner that moves the sample and a separate Z-actuatorthat moves the probe. The instrument is thus capable of creatingrelative motion between the probe and the sample while measuring thetopography or some other surface property of the sample as described,e.g., in Hansma et al. U.S. Pat. No. RE 34,489; Elings et al. U.S. Pat.No. 5,266,801; and Elings et al. U.S. Pat. No. 5,412,980.

In a common configuration, probe 14 is often coupled to an oscillatingactuator or drive 16 that is used to drive probe 14 at or near aresonant frequency of cantilever 15. Alternative arrangements measurethe deflection, torsion, or other motion of cantilever 15. Probe 14 isoften a microfabricated cantilever with an integrated tip 17.

Commonly, an electronic signal is applied from an AC signal source 18under control of an SPM controller 20 to cause actuator 16 (oralternatively XYZ scanner) to drive the probe 14 to oscillate. Theprobe-sample interaction is typically controlled via feedback bycontroller 20. Notably, the actuator 16 may be coupled to the XYZscanner and probe 14 but may be formed integrally with the cantilever 15of probe 14 as part of a self-actuated cantilever/probe.

Often a selected probe 14 is oscillated and brought into contact withsample 22 as sample characteristics are monitored by detecting changesin one or more characteristics of the oscillation of probe 14, asdescribed above. In this regard, a deflection detection apparatus 25 istypically employed to direct a beam towards the backside of probe 14,the beam then being reflected towards a detector 26. As the beamtranslates across detector 26, appropriate signals are processed atblock 28 to, for example, determine RMS deflection and transmit the sameto controller 20, which processes the signals to determine changes inthe oscillation of probe 14. In general, controller 20 generates controlsignals to maintain a relative constant interaction between the tip andsample (or deflection of the lever 15), typically to maintain a setpointcharacteristic of the oscillation of probe 14. More particularly,controller 20 may include a PI Gain Control block 32 and a High VoltageAmplifier 34 that condition an error signal obtained by comparing, withcircuit 30, a signal corresponding to probe deflection caused bytip-sample interaction with a setpoint. For example, controller 20 isoften used to maintain the oscillation amplitude at a setpoint value,AS, to insure a generally constant force between the tip and sample.Alternatively, a setpoint phase or frequency may be used.

A workstation 40 is also provided, in the controller 20 and/or in aseparate controller or system of connected or stand-alone controllers,that receives the collected data from the controller and manipulates thedata obtained during scanning to perform point selection, curve fitting,and distance determining operations.

The deflection of the cantilever in response to the probe tip'sinteraction with the sample is measured with an extremely sensitivedeflection detector, most often an optical lever system. In such opticalsystems, a lens is employed to focus a laser beam, from a sourcetypically placed overhead of the cantilever, onto the back side of thecantilever. The backside of the lever (the side opposite the tip) isreflective (for example, using metalization during fabrication) so thatthe beam may be reflected therefrom towards a photodetector. Thetranslation of the beam across the detector during operation provides ameasure of the deflection of the lever, which again is indicative of oneor more sample characteristics.

In nanoindentation experiments using AFM, the tip of the probe isrelatively dull, unlike probes employed in typical AFM which have sharptips (radius less than 10 nm). A nanoindentation probe has a tip radiusthat is preferably about a micron. Moreover, the apex is preferablysubstantially spherical. Some known indentation tips are rugged, suchthat profiling can be performed, but with low resolution. Such tips maybe used to measure step heights, but nanoscale topography is notpossible.

To nanoindent very small volume samples and obtain good resolution data,researchers often employ diamond-tipped probes or coated AFM tips. Inthe end, nanoindentation requires probes that are sufficiently strong towithstand the pressures exerted on samples of varying hardness. Theapexes of these tips are typically irregularly shaped, making itdifficult to accurately correlate displacement to force, therebyintroducing error to the desired material characteristic measurement.

Typically, for nanoindentation, users purchase tipless AFM probes andattach tiny spheres to the distal or free end of the cantilever. Thetiny spheres may be made of a variety of materials depending on theusers' application. This attachment operation is performed on aprobe-by-probe basis, and therefore, is time-consuming and costly. Inthis regard, the spheres are most often glued to the levers which leadto a slew of potential issues. First and foremost, the integrity of thebond must be considered as the tips are caused to repeatedly impactsamples of varying hardness. Also, the application of the glue itself tothese small scale spheres is difficult. Care needs to be taken to makesure no glue remains on the surfaces of the probe tip that interact withthe sample, as any extra material can alter the nanoindentationmeasurement. Moreover, because these expensive AFM tips can getcontaminated during nanoindentation experiments, users often want toclean them for re-use. Typically, a solvent is used, which may not agreewith the glue, and compromise the bond. Overall, the attachment processis complicated and costly, with non-ideal yield and limitations onre-use.

In another alternative, it is known to “blunt” the end of a standard AFMtip. In this case, the sharp AFM tip is dulled using high temperaturereforming of the apex. This often requires re-filling at least a portionof the apex with silicon to re-shape it, a difficult process, often withuncertain results. In addition, the achievable tip radii are in therange of 150-900 nm (less than the desired 1 μm for nanoindentation).The re-filling process can be used to make the radius larger, but thenit is difficult to maintain the desired spherical shape. And, like theother known options, this technique is performed on a probe-by-probebasis, and thus is also time-consuming and costly.

In yet another alternative, electronic beam deposition (EBD) (e-beamdeposited carbon) and Scanning Electron Microscopy (SEM) may be used toform the spheres on probe cantilevers. Similar to the problems of theother probe solutions, this option is time-consuming and expensive, andthe yield of high integrity probes is often low. SEMs are million plusdollar tools employing sophisticated equipment (e.g., alignment tools).The process is extremely slow as one probe at a time is made. Inaddition, most often the resulting tip radius is still sub-micron. Ifthe probe is attempted to be made larger, the ball becomes lessspherical (oblong even)—which is non-ideal for the precise materialproperty tests contemplated by the present preferred embodiments.Cleaning of these types of tips is difficult, if not impossible.

In view of the above, the field of nanoindentation using AFM was in needof a probe that overcomes the above-noted drawbacks related tomaintaining a spherical apex, as well as cost of manufacture anddurability. More particularly, a probe suitable for nanoindentation andhaving a spherically-shaped apex, a tip radius of about 1 μm, andcapable of being batch fabricated was desired.

Note that “SPM” and the acronyms for the specific types of SPM's, may beused herein to refer to either the microscope apparatus, or theassociated technique, e.g., “atomic force microscopy.”

SUMMARY OF THE INVENTION

The preferred embodiments overcome the drawbacks of prior solutions byproviding a nanoindentation probe and corresponding method ofmanufacture that uses photolithographic techniques to define a post andthen deposit a material capable of being conformally deposited on thepost. This deposition (e.g., LPCVD) develops a hemispherical distal endat the tip of the probe. Large radius probes made according to thepresent techniques are batch fabricated and thus are less costly. Themicrofabrication process yields bulk probes with high integrity. Also,no spheres need to be attached to the AFM tip, nor do the spheres needto be machined (“blunted”) from existing tips or formed using highlysophisticated tools (e.g., SEM).

According to a first aspect of the preferred embodiment, a method ofbatch-fabricating probes for a surface analysis instrument includesproviding a substrate and forming an array of posts from the substrate.Then, the method includes depositing tip material on the posts so as tocreate a hemispherical cap on each post. After the tip material isremoved around the cap, a cantilever for each cap is formed.

According to another aspect of the preferred embodiment, the formingstep includes patterning an array of cylindrical photoresist features onthe substrate, etching the substrate and then removing the photoresistfeatures so as to reveal the array of posts.

In a further aspect of this embodiment, the posts are substantiallycylindrical with or without a pointed apex. Further, a width of theposts is preferably narrowed. This may be done by isotropically etchingthe posts or consuming the post material by oxidation and etch.

According to a still further aspect of the preferred embodiment, the tipmaterial is any material that can be conformally deposited. For example,the tip material may be silicon nitride.

In another aspect of the preferred embodiment, the cap defines a tip ofthe probe, and a radius of the tip is at least ¼ micron. Preferably, thetip radius is at least 1 micron.

In another aspect of this embodiment, parameters of the substrate etchare selected so as to form the posts with a flared base.

According to a still further aspect of the preferred embodiment, thecantilever is formed either from the tip material itself or from thesilicon material underneath the cap.

In another aspect of this embodiment, the hemispherical caps form theapex of high aspect ratio tips. Further, the tips may be tilted toaccommodate mounting the probe in the surface analysis instrument.

According to a further aspect of the preferred embodiment, a largeradius AFM probe is microfabricated according to a process including thesteps of providing a substrate and forming an array of posts from thesubstrate. Tip material is then deposited on the posts so as to create ahemispherical cap on each post. The tip material is removed around thecap and a cantilever is formed for each cap.

These and other objects, features, and advantages of the invention willbecome apparent to those skilled in the art from the following detaileddescription and the accompanying drawings. It should be understood,however, that the detailed description and specific examples, whileindicating preferred embodiments of the present invention, are given byway of illustration and not of limitation. Many changes andmodifications may be made within the scope of the present inventionwithout departing from the spirit thereof, and the invention includesall such modifications.

BRIEF DESCRIPTION OF THE DRAWINGS

A preferred exemplary embodiment of the invention is illustrated in theaccompanying drawings in which like reference numerals represent likeparts throughout, and in which:

FIG. 1 is a schematic illustration of a Prior Art atomic forcemicroscope;

FIG. 2 is a schematic side elevational view of a probe having a lowaspect ratio tip and a hemispherical apex, according to a preferredembodiment;

FIG. 3 is a schematic side elevational view of a probe having a tip witha hemispherical apex and a flared base, according to another preferredembodiment;

FIG. 4 is a schematic side elevational view of a probe having ahigh-aspect ratio tip and hemispherical apex;

FIGS. 5A-5F are a series of images of the stepwise microfabrication ofAFM probes with large radius tips, according to a method of thepreferred embodiments;

FIG. 6 is a flow chart of a method to batch fabricate large radiusprobes of the type shown in FIG. 2, according to a preferred embodiment;

FIG. 7 is an image of a probe produced using the method of FIG. 6, witha silicon lever;

FIG. 8 is an image of a probe produced using the method of FIG. 6, witha silicon nitride lever;

FIG. 9 is an image of a high aspect ratio post structure used to producea probe such as that shown in FIGS. 7 and 8;

FIG. 10 is an image of a post structure similar to FIG. 9, but with aflared base;

FIG. 11 is a side elevational image of a LPCVD silicon nitridedeposition on a post structure such as that shown in FIG. 9;

FIG. 12 is a perspective image of an LPCVD silicon nitride deposition ona post structure such as that shown in FIG. 10;

FIG. 13 is a schematic side elevational view of a probe similar to theprobe of FIG. 2, but with a platform between the cantilever and lowaspect ratio tip;

FIG. 14 is a schematic side elevational view of a probe having ahigh-aspect ratio tip similar to FIG. 4, but produced with a tilt toaccommodate angled mounting of the probe in an AFM; and

FIG. 15 is a schematic side elevational view of a probe having afunctionalized tip with a flared base.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring initially to FIG. 2, probe 50 for use in an atomic forcemicroscope and microfabricated according to the preferred embodiments isschematically shown. Probe 50 includes a cantilever 52 made of, e.g.,silicon, that may be photolithographically patterned on a silicon wafer(i.e., the substrate). Probe 50 includes a tip 54 supported at a freeend 56 of cantilever 52. Tip 54 has a large radius (“r”), on the orderof about one (1) micron, but may have a radius as small as ¼ micron andas large as 25 microns. Tip 54 of FIG. 2 is a robust low aspect ratiotip and therefore is suitable not only for nanoindentation, but lowresolution imaging.

Tip 54 has a proximal end 58 that interfaces free end 56 of cantilever52, and a distal end 60 that extends from free end 56 and is configuredto interact with a sample (not shown). Distal end 60 of tip 54 has ahemispherical-shaped apex produced according to the methods describedherein. Most generally, a selected tip material (e.g., silicon nitride)is built up on a post or spike (e.g., FIG. 9) that has been formed(e.g., photolithographically) from, for example, the silicon wafer.Importantly, unlike known techniques, which produce probes one-by-one,probe 50 is batch fabricated so the portion of tip 54 (i.e., distal end60) that interacts with the sample does not have to be attached to astandard AFM cantilever or tip (glued or otherwise), or modified from anexisting AFM tip.

Turning to FIG. 3, a probe 70 having a cantilever 72 formed from asubstrate (e.g., photolithographically patterned on a silicon wafer)includes a free end 74 supporting a large radius tip 76. Tip 76 includesa distal end 78 (i.e., apex) having a hemispherical shape and a large,micron sized radius, and a conical or pyramidal shaped base or body 80.Tip 76 also sits on a platform or base 82 made of the same material astip 76 (for example, silicon nitride) that is deposited on the siliconwafer during formation of tip 76, as described further below. Thefunnel-shaped body 80 of tip 76 is formed by starting with acorrespondingly shaped post or spike (described further below) andselecting certain material deposition parameters. The flared body 80provides support for particular applications in which a high aspectratio tip is required and the risk of shearing or otherwise breakingapex of tip 76 off probe 70 is high (harder samples, etc). Tall tipswithout the flared base are more flexible and may experience undesiredlateral displacement in certain applications.

FIG. 4 illustrates a probe 90 manufactured according to the disclosedmethods, similar to the large radius low-aspect ratio tip of probe 50 ofFIG. 2. Probe 90 includes a cantilever 92 having a free end 94supporting a tip 95. Tip 95 has a hemispherical apex 96 and has aplatform 97 formed during manufacture (e.g., using LPCVD to conformallydeposit Si₃N₄), as described below. Unlike probe 70 and itsfunnel-shaped body 80, tip 95 is a high aspect ratio tip having anelongate body 98 with a substantially uniform width along its length.This style tip is preferred for example, for deep trench samples orsamples with high aspect ratio walls where interference from a flaredbase or the cantilever itself needs to be avoided.

The series of schematic drawings shown in FIGS. 5A-5F illustrate a probeas it is being batch-fabricated according to one method of the preferredembodiments. The process yields an array of probes having large radiushemispherical tips. As noted previously, a post or spike is formed firstand provides the structure upon which tip material will be deposited.Starting with FIG. 5A, a substrate 130 (e.g., a silicon wafer with orwithout a surface material such as but not limited to an oxide, nitride,metallic or composite film) is provided and a layer of photoresist (notshown) is applied thereon. Using an appropriate mask, an array ofphotoresist structures (e.g., cylinders) for etching the posts uponwhich the tips of the probes will be formed is patterned on thephotoresist. After an appropriate selective chemical dissolution of thephotoresist, an array of photoresist posts 132 remains with widthsbetween ½ micron and 10 microns and heights between ¼ micron and 30microns. Turning to FIG. 5B, the silicon wafer 130 is then etched(dry/wet) using the photoresist structures 132 as a mask. What remainsis an array of silicon posts 134, with the photoresist cylinders 132residing thereon. Once the photoresist cylinders 132 are removed, anarray of silicon structures (FIG. 5C) remains. These posts 134 willprovide a base structure for the fabrication of the probe tips.

Next, in FIG. 5D, an isotropic etch may be employed to narrow the width“w” of the silicon structure 134 from about 1.5 μm to about ¼ micron,for example, essentially creating a sub-micron silicon post or spike.Although posts made of silicon are described herein, the posts may befabricated from deposited nitride or oxide, for example. The resultantspike is generally uniform along its entire width; the width of the postis in the range of about ¼ micron.

In FIG. 5E, after placing the wafer in a furnace, LPCVD of siliconnitride 135 (2.95 μm, for example) can be used to create a hemisphericalcap 136 around the silicon posts or spikes 134 of the array. Notably,silicon nitride is one preferred material, but any material capable ofproviding a conformal coating on posts 134 may be utilized. The radiusof hemispherical caps 136 can be in the range of about ¼ micron up toabout 25 μm. The actual radius will be dependent on how long the film isdeposited on the posts, as understood in the art.

Turning next to FIG. 5F, some of the silicon nitride 135 isphotolithographically removed using an appropriate mask, protecting tipwith cap 136 and leaving a platform 138 of silicon nitride between thetip and substrate 130. Platform 138 is a natural artifact of the processand will influence the cantilever's frequency depending on itsdimensions. In this regard, the dimensions will influence the weight oftip 136; the larger platform 138, the lower the resonant frequency.Finally, a cantilever 140 is made, preferably using photolithography aswell. An appropriate mask is employed to pattern cantilevers 140, makingsure to align tips 136 near the distal or free end of the levers. Aplasma etch of the silicon wafer may be used to define cantilevers 140.Then, a backside etch (e.g., KOH) may be used to simultaneously releasethe freestanding cantilevers and define the probe bodies.

Turning to FIG. 6, a method 200 of batch fabricating large radiusprobes, such as those shown in FIGS. 2-4 is shown. Method 200 will bedescribed in conjunction with FIGS. 5A-5F to illustrate the probe build.Method 200 includes a first step, Block 202, of providing a substrate, asilicon wafer, for example (130 in FIG. 5A). The wafer is used as asubstrate for coating a photoresist in Block 204. An appropriate mask isused to create photoresist structures (132 in FIG. 5A) that will be usedas a mask to create silicon posts. Photoresist structures have anappropriate width that will at least partially dictate the size of theradius of the tips. Next, using lithography in Block 206, posts arefabricated using, e.g., a chemical etch (FIG. 5B). Posts provide thestructure upon which the tip material is deposited to form the largeradius apex of the tips. Once the posts are built, the photoresist isremoved in Block 208 (post 134 in FIG. 5C). The image transfer is usedto create the silicon spikes. After a lithography step to mask the waferfor production of the spike, a dry etch of the silicon is performed.This provides a deep etch into the silicon without losing uniformity inthe width or diameter of the spike. In the end, high aspect ratio spikesare produced uniformly across the wafer using silicon, oxide, or anitride.

Next, in Block 210, the resulting posts are shaped (e.g., to narrowtheir width) using known dry or wet etch techniques (FIG. 5D). Thenitride is then deposited to begin to form the tip in Block 212. As thenitride is deposited, it coats the entire wafer including around theposts (135 in FIG. 5E). This silicon nitride begins to build around theposts and form the tip. Ultimately, a tip 136 having a cap defining ahemispherical apex 137 is produced (FIG. 5E).

In Block 214, a platform or base for the tip is formed using anappropriate mask and removing the nitride layer. Platform 138 typicallyis round (FIG. 5F) with a diameter that is several microns wider thanthe width of the tip/base structure. Variations in the diameter of theplatform can be used to target the cantilever's frequency withoutaffecting its stiffness. This is preferably done with photolithographybut other known methods may be used. Next, the process includes a step(Block 216) to define the cantilever using, e.g., suitable appropriatephotolithography techniques. Once the cantilever is defined, an etch isperformed in Block 218 to produce the cantilever (140 in FIG. 5F).Finally, in Block 220, the probes are released from the wafer (e.g.backside etch) producing the resultant large radius probes.

Using the method of FIG. 6 described in connection with FIG. 5A-5F,indentation probes of different types can be produced. Turning to FIG.7, an image of a nanoindentation probe 300 with a silicon nitride tip302 and platform 304, as well as a silicon lever 306 is shown. This is astiffer version of the probe. In FIG. 8, a nanoindentation probe 310with a silicon nitride tip 312 and platform 314, as well as lever 316 isshown in the image. This is a lower stiffness (lower spring constant,e.g., for softer samples) probe. Each probe is made with the postdeveloped first (post 313 can be seen in FIG. 8) and then the nitridedeposited thereon. The difference between probe 300 with the siliconlever 306 (FIG. 7) and probe 310 with nitride lever 316 (FIG. 8), is theformation of the cantilever itself. In one example, silicon cantilever306 is patterned on the silicon wafer (substrate) itself. The nitridelever 316 of FIG. 8, on the other hand, is formed from the depositednitride material used to build the tip. Notably, the nitride lever inthis case is shaped to include a midsection 318 of greater width thanthe proximal end of the lever attached to the base of the assembly aswell as the distal end of the lever supporting the tip.

Additional images showing the process and the different types of poststructures and hemispherical structures developed are illustrated inFIGS. 9-12. In FIG. 9, a post structure 350 having a substantiallyuniform width “w” along its entire length is shown. Such posts aretypically about a ¼ micron wide, but they can be more narrow. The radiusof the tip that is ultimately developed using post 350 can be sub-micronup to 25 microns. The post 350 shown in FIG. 9 provides a high aspectratio tip which is defined by essentially having at least a 5:1 heightto width ratio, and more preferably, a 10:1 height to width ratio. Anon-high aspect ratio tip is typically about 1:1. Ultimately, a highaspect ratio tip is produced using a post (FIG. 9) with a controlleddiameter across the entire wafer so that the probes can be batchfabricated.

For additional strength, a post structure 360 with a bottom flare 362may be developed (see also, schematic probe 70 of FIG. 3), as shown inFIG. 10. This is typically preferred when a tall or high aspect ratiotip is required and the risk of shearing or otherwise breaking apex oftip off probe is high (harder samples, etc). Tall tips without theflared base are more flexible and may experience undesired lateraldisplacement in certain applications.

As shown in FIG. 11, an image of a hemispherical tip 400 produced on apost (350 in FIG. 9) is shown. This structure was made with a 2.90micron LPCVD nitride deposition. In FIG. 12, an image of a tip 410 withhemispherical apex and flared base 412 (similar to funnel-shaped body 80of schematic probe 70—FIG. 3) sitting atop a platform 414 of materialconformally deposited on a silicon substrate (wafer) 416. Tip 410 isproduced on a post with a flare structure using a 3.36 micron LPCVDnitride deposition. Again, for particular applications, tips with flaredbases may be preferred.

In FIG. 13, a probe 430 having a low aspect ratio tip 432, a platform434, and cantilever 436, is shown. In this case, for particularapplications, surface scanning can still be employed because the tip ismore robust given its lower aspect ratio. The resolution is not nearlythe same as a typical AFM, but continuous scanning can still be used toproduce an AFM image. In FIG. 14, a probe 440 having a tip 442 that sitson a platform 444 (tip 442 and platform 444 deposited on a, e.g.,silicon substrate that is patterned to produce cantilevers 446) istilted at a selected angle using an appropriate masking and/or etchingtechnique. Such a tip may be preferred when the mount for the probeassembly situates the tip at an angle relative to the surface of thesample. With the tilted tip, the engage angle between the apex of thetip and the sample can be modified so that it interacts orthogonallywith the sample surface. Finally, in FIG. 15, a probe 500 is shownhaving a lever 502 with a tip 504 having a flared body or base 506. Inthis case, tip 504 is functionalized for particular applications. Forexample, if performing a nanoindentation experiment in a harshenvironment, the tip might be at risk of being dissolved. Therefore, acoating 508 such as chrome or gold may be deposited on tip 504 tomaintain the integrity of the tip. Adhesive interaction between thesample and tip may be of interest. Such coatings may enhance the user'sability to investigate this property. The coating 508 can be applied tothe other tip structures and not limited to just the flared basestructure.

Although the best mode contemplated by the inventors of carrying out thepresent invention is disclosed above, practice of the present inventionis not limited thereto. It will be manifest that various additions,modifications and rearrangements of the features of the presentinvention may be made without deviating from the spirit and scope of theunderlying inventive concept.

What is claimed is:
 1. An AFM probe microfabricated by a processcomprising the steps of: providing a substrate; forming an array ofcylindrical posts from the substrate; depositing tip material on theposts so as to create a hemispherical cap on each post; removing the tipmaterial around the cap to form a tip wherein the hemispherical cap hasa radius greater than ¼ μm; and forming a cantilever for each cap,wherein the tip is a high aspect ratio tip with a height to width ratioof at least 5:1.
 2. The probe of claim 1, wherein the forming stepincludes patterning an array of cylindrical photoresist features on thesubstrate, etching the substrate using the array of cylindricalphotoresist features as a mask and then removing the photoresistfeatures so as to reveal the array of posts.
 3. The probe of claim 1,wherein the cap defines a tip of the probe, and a radius of the tip isat least ¼ micron.
 4. The probe of claim 1, wherein the aspect ratio isgreater than 10:1.